U.S. patent application number 15/303292 was filed with the patent office on 2017-02-02 for eddy current array probe with independent transmitters.
This patent application is currently assigned to EDDYFI NDT INC.. The applicant listed for this patent is EddyFI NDT Inc.. Invention is credited to Nathan DECOURCELLE, Marc GRENIER, Stefan PARMENTIER, Michael SIROIS.
Application Number | 20170030862 15/303292 |
Document ID | / |
Family ID | 54323551 |
Filed Date | 2017-02-02 |
United States Patent
Application |
20170030862 |
Kind Code |
A1 |
SIROIS; Michael ; et
al. |
February 2, 2017 |
Eddy Current Array Probe With Independent Transmitters
Abstract
There is described an eddy current array probe for detection and
depth sizing of a surface- breaking defect in a metallic material,
said eddy current array probe comprising: a probe body comprising a
plurality of probe elements arranged in a linear configuration, the
probe elements each comprising at least one coil, the probe body
being adapted to be displaced along a surface of the metallic
material so that a longitudinal axis of the coil be parallel to the
surface of the metallic material, the coil, when in use, being
adapted to induce an eddy current within the metallic material
detect the eddy current; and a set of active elements of the
plurality of probe elements being adapted to be selectively
operated at a plurality of time-spaced instances.
Inventors: |
SIROIS; Michael; (Quebec,
CA) ; PARMENTIER; Stefan; (Quebec, CA) ;
GRENIER; Marc; (Quebec, CA) ; DECOURCELLE;
Nathan; (Blyes, FR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
EddyFI NDT Inc. |
Quebec |
|
CA |
|
|
Assignee: |
EDDYFI NDT INC.
Quebec
QC
|
Family ID: |
54323551 |
Appl. No.: |
15/303292 |
Filed: |
April 14, 2015 |
PCT Filed: |
April 14, 2015 |
PCT NO: |
PCT/IB2015/052722 |
371 Date: |
October 11, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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61979352 |
Apr 14, 2014 |
|
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G01N 27/902 20130101;
G01N 27/9033 20130101; G01N 27/904 20130101 |
International
Class: |
G01N 27/90 20060101
G01N027/90 |
Claims
1. An eddy current array probe for detection and depth sizing of a
surface-breaking defect in a metallic material, said eddy current
array probe comprising: a probe body comprising a plurality of
probe elements arranged in a linear configuration, the probe
elements each comprising at least one coil, the probe body being
adapted to be displaced along a surface of the metallic material so
that a longitudinal axis of the coil be parallel to the surface of
the metallic material, the coil, when in use, being adapted to
induce an eddy current within the metallic material and detect the
eddy current; and a set of active elements of the plurality of
probe elements being adapted to be selectively operated at a
plurality of time-spaced instances.
2. The eddy current array probe of claim 1, wherein the at least
one coil comprises a transmitter coil and a receiver, the
transmitter coil, when in use, being adapted to induce an eddy
current within the metallic material, and a longitudinal axis of
the receiver being substantially orthogonal to the eddy current and
substantially parallel to the surface of the metallic material so
as to allow the receiver to detect the eddy current.
3. The eddy current array probe of claim 2, wherein the receiver
comprises a receiver coil.
4. The eddy current array probe of claim 2, wherein the receiver
comprises one of a Hall effect sensor and a magnetoresistance
sensor.
5. The eddy current array probe of claim 2, wherein a longitudinal
axis of the transmitter coil is parallel to the longitudinal axis
of the receiver.
6. The eddy current array probe of claim 5, wherein the transmitter
coil and the receiver are concentric.
7. The eddy current array probe of claim 6, wherein the probe
elements each further comprise a core extending between two ends,
the transmitter coil being mounted on the core and the magnetic
field being generated between the two ends of the core.
8. The eddy current array probe of claim 7, wherein the core
further comprises two legs each extending from a respective one of
the two ends for guiding the magnetic field towards the surface of
the metallic material.
9. The eddy current array probe of claim 7, wherein the receiver is
mounted on the transmitter coil.
10. The eddy current array probe of claim 7, wherein the probe
elements each further comprise a sensing coil for detecting an end
of the surface-breaking defect, a longitudinal axis of the sensing
coil being orthogonal to the eddy current and the surface of the
metallic material.
11. The eddy current array probe of claim 2, wherein, for each
active element, at least one of the respective transmitter coil is
activated to generate the magnetic field and the respective
receiver is activated to detect the eddy current.
12. The eddy current array probe of claim 2, wherein, at each one
of the time-spaced instances, two following ones of said active
elements are spaced apart by at least one inactive element of said
plurality of probe elements.
13. The eddy current array probe of claim 2, wherein the set of
active elements comprises at least one group of at least three
adjacent probe elements contained within the plurality of probe
elements, the transmitter coil of each one of the at least three
adjacent probe elements being activated and the receiver of a
central one of at least the three adjacent probes being
activated.
14. The eddy current array probe of claim 13, wherein the set of
active elements comprises at least two groups of at least three
adjacent probes, the at least two groups being spaced apart by at
least one inactive probe element of said plurality of probe
elements.
15. The eddy current array probe of claim 2, wherein the set of
active elements comprises at least one group of at least three
adjacent probes contained within the plurality of probe elements,
the receiver of each one of the at least three adjacent probes
being activated and the transmitter coil of a central one of at
least the three adjacent probes being activated.
16. The eddy current array probe of claim 15, wherein the set of
active elements comprises at least two groups of at least three
adjacent probes, the at least two groups being spaced apart by at
least one inactive probe element of said plurality of probe
elements.
17. The eddy current array probe of claim 1, wherein each one of
the probe elements is encapsulated in a respective casing having a
surface-contacting face adapted to contact the surface of the
metallic material.
18. The eddy current array probe of claim 1, wherein each one of
the probe elements is adapted to move independently towards and
away from the surface to accommodate for geometry variations of the
surface of the material.
19. The eddy current array probe of claim 16, further comprising a
frame and a plurality of springs each having a first end secured to
the frame and a second frame secured to a respective one of the
probe elements.
20. A method for scanning a surface of a metallic material,
comprising: providing an eddy current array probe comprising: a
probe body comprising a plurality of probe elements arranged in a
linear configuration, the probe elements each comprising at least
one coil, the probe body being adapted to be displaced along a
surface of the metallic material so that a longitudinal axis of the
coil be parallel to the surface of the metallic material, the coil,
when in use, being adapted to induce an eddy current within the
metallic material and detect the eddy current and a set of active
elements of the plurality of probe elements being adapted to be
selectively operated at a plurality of time-spaced instances;
positioning the eddy current array probe on the surface at a first
position; selectively activating the active elements at the
plurality of time-spaced instances according to a first activation
sequence, thereby generating and measuring a first plurality of
eddy currents within the metallic material; moving the eddy current
array probe to a second and different position; and selectively
activating the active elements at the plurality of time-spaced
instances according to a second activation sequence, thereby
generating and measuring a second plurality of eddy currents within
the metallic material.
21. The method of claim 20, wherein the first and second activation
sequences are identical.
22. The method of claim 20, wherein said selectively activating
comprises sequentially activating groups of probe elements at
different ones of the time-spaced instances, each group of probe
elements comprising at least one probe element for which the
transmitter coil is activated and the receiver is activated, an
identification of the at least one probe element varying from one
of the time-spaced instances to another one of the time-spaced
instances.
23. The method of claim 22, wherein the at least one probe element
comprises at least two probe elements, two following ones of the at
least two probe elements being spaced apart by an inactive probe
element at each one of the time-spaced instances.
24. The method of claim 20, wherein said selectively activating
comprises sequentially activating groups of probe elements at
different ones of the time-spaced instances, each group of probe
elements comprising at least one set of at least three adjacent
probes, the receiver of each one of the at least three adjacent
probes being activated and the transmitter coil of a central one of
at least the three adjacent probes being activated concurrently
with the activation of the receiver.
25. The method of claim 24, wherein the at least one set of at
least three adjacent probe elements comprises a first set of at
least three probe elements and a second set of at least three probe
elements, the first and second sets being spaced apart by at least
one inactive probe element at each one of the time-spaced
instances.
26. The method of claim 20, wherein said selectively activating
comprises sequentially activating groups of probe elements at
different ones of the time-spaced instances, each group of probe
elements comprising at least one set of at least three adjacent
probes, the transmitter coil of each one of the at least three
adjacent probes being activated and the receiver of a central one
of at least the three adjacent probes being activated concurrently
with the activation of the receiver.
27. The method of claim 26, wherein the at least one set of at
least three adjacent probe elements comprises a first set of at
least three probe elements and a second set of at least three probe
elements, the first and second sets being spaced apart by at least
one inactive probe element at each one of the time-spaced
instances.
28. The method of claim 20, wherein said metallic material
comprises a non-metallic surface coating.
29. The method of claim 20, wherein said moving is performed
substantially continuously.
Description
TECHNICAL FIELD
[0001] The present invention relates to nondestructive testing, and
particularly to high-resolution Eddy Current Array (ECA) probes for
the detection and sizing of surface-breaking defects in metals.
BACKGROUND OF THE ART
[0002] Nondestructive Testing (NDT) is a discipline which aims at
evaluating the integrity and/or physical properties of materials
without permanently altering the article being inspected. There are
numerous NDT methods. Electromagnetic Testing (ET) techniques
essentially induce electric currents and/or magnetic fields inside
the article being inspected, and assess its integrity and/or
physical properties based on the electromagnetic response
obtained.
[0003] One particular application of ET techniques relates to
surface-breaking defects occurring in metallic objects. Detecting
and/or characterizing surface defects such as cracks is paramount
in a number of industries, and across a variety of applications
such as weld verification or condition monitoring of pipelines or
pressure vessels.
[0004] One of the most common ET techniques is referred to as Eddy
Current Testing (ECT) and a probe using this technique is referred
to as an ECT probe or a "Weld Probe". An ECT probe usually
comprises a small active area in the order of a few square
millimeters. Due to its small active area, an ECT probe usually has
to be manipulated with precision when a large region of interest
needs to be examined. Raster scanning is typical in order to
effectively cover an area such as a weld while using an ECT probe.
Therefore, the use of an ECT probe requires dexterity from the
operator and is time-consuming if a large area has to be scanned
requires sufficient time to cover a large area while scanning just
a few square millimeters at a time. Indeed, these probes are often
referred to as "pencil probes" for the shape they exhibit.
[0005] Furthermore, an ECT probe is usually designed so as to
minimize the lift-off signal produced, for example, by a layer of
paint or coating laying over the metallic object to be inspected,
rather than at quantifying this lift-off. Therefore, information
about the layer of paint or coating such as its thickness cannot be
measured while using an ECT probe.
[0006] Balanced Field Electromagnetic Technique (BFET) probes may
also be used to detect defects in a material. However, BFET probes
presents similar limitations with respect to ECT probes.
[0007] Alternating Current Field Measurement (ACFM) probes have
also been developed to detect defects in a material. Some ACFM
probes make use of a single, large transmitter, which induces a
widespread magnetic field in the material being examined. At least
some of the above-described limitations also apply to ACFM
probes.
[0008] Eddy Current Array (ECA) probes may also be used to detect
defects in a material. An ECA probe is composed of several
individual coils grouped together in one assembly. ECA probes
typically feature several rows of coils that can be excited in
sequence (multiplexed) to maximize the coverage, minimize the
interference between coils in close proximity (mutual inductance),
and maximize the resolution of the probe. Some ECA probes comprise
orthogonal coils, which prevents the use of the lift-off signal for
characterization of a defect over a non-metallic coating. Other ECA
probes comprise pancake coils. However, such ECA probes are usually
not suitable for providing quality signals on many common materials
such as ferritic steel and in the situation where there is a
non-magnetic coating over the material to be inspected.
[0009] Therefore, there is a need for an improved eddy current
probe.
SUMMARY
[0010] According to a broad aspect, there is provided an eddy
current array probe for detection and depth sizing of a
surface-breaking defect in a metallic material, said eddy current
array probe comprising: a probe body comprising a plurality of
probe elements arranged in a linear configuration, the probe
elements each comprising at least one coil, the probe body being
adapted to be displaced along a surface of the metallic material so
that a longitudinal axis of the coil be parallel to the surface of
the metallic material, the coil, when in use, being adapted to
induce an eddy current within the metallic material and detect the
eddy current; and a set of active elements of the plurality of
probe elements being adapted to be selectively operated at a
plurality of time-spaced instances.
[0011] In one embodiment, the at least one coil comprises a
transmitter coil and a receiver, the transmitter coil, when in use,
being adapted to induce an eddy current within the metallic
material, and a longitudinal axis of the receiver being
substantially orthogonal to the eddy current and substantially
parallel to the surface of the metallic material so as to allow the
receiver to detect the eddy current.
[0012] In one embodiment, the receiver comprises a receiver
coil.
[0013] In another embodiment, the receiver comprises one of a Hall
effect sensor and a magneto-resistance sensor.
[0014] In one embodiment, a longitudinal axis of the transmitter
coil is parallel to the longitudinal axis of the receiver.
[0015] In one embodiment, the transmitter coil and the receiver are
concentric.
[0016] In one embodiment, the probe elements each further comprise
a core extending between two ends, the transmitter coil being
mounted on the core and the magnetic field being generated between
the two ends of the core.
[0017] In one embodiment, the core further comprises two legs each
extending from a respective one of the two ends for guiding the
magnetic field towards the surface of the metallic material.
[0018] In one embodiment, the receiver is mounted on the
transmitter coil.
[0019] In one embodiment, the probe elements each further comprise
a sensing coil for detecting an end of the surface-breaking defect,
a longitudinal axis of the sensing coil being orthogonal to the
eddy current and the surface of the metallic material.
[0020] In one embodiment, for each active element, the respective
transmitter coil is activated to generate the magnetic field and/or
the respective receiver is activated to detect the eddy
current.
[0021] In one embodiment, at each one of the time-spaced instances,
two following one of said active elements are spaced apart by at
least one inactive element of said plurality of probe elements.
[0022] In another embodiment, the set of active elements comprises
at least one group of at least three adjacent probe elements
contained within the plurality of probe elements, the transmitter
coil of each one of the at least three adjacent probe elements
being activated and the receiver of a central one of at least the
three adjacent probes being activated.
[0023] In one embodiment, the set of active elements comprises at
least two groups of at least three adjacent probes, the at least
two groups being spaced apart by at least one inactive probe
element of said plurality of probe elements.
[0024] In a further embodiment, the set of active elements
comprises at least one group of at least three adjacent probes
contained within the plurality of probe elements, the receiver of
each one of the at least three adjacent probes being activated and
the transmitter coil of a central one of at least the three
adjacent probes being activated.
[0025] In one embodiment, the set of active elements comprises at
least two groups of at least three adjacent probes, the at least
two groups being spaced apart by at least one inactive probe
element of said plurality of probe elements.
[0026] In one embodiment, each one of the probe elements is
encapsulated in a respective casing having a surface-contacting
face adapted to contact the surface of the metallic material.
[0027] In one embodiment, each one of the probe elements is adapted
to move independently towards and away from the surface to
accommodate for geometry variations of the surface of the
material.
[0028] In one embodiment, the array probe further comprises a frame
and a plurality of springs each having a first end secured to the
frame and a second frame secured to a respective one of the probe
elements.
[0029] According to another broad aspect, there is provided a
method for scanning a surface of a metallic material using the eddy
current array probe, comprising: positioning the eddy current array
probe on the surface at a first position; selectively activating
the active elements at the plurality of time-spaced instances
according to a first activation sequence, thereby generating and
measuring a first plurality of eddy currents within the metallic
material; moving the eddy current array probe to a second and
different position; and selectively activating the active elements
at the plurality of time-spaced instances according to a second
activation sequence, thereby generating and measuring a second
plurality of eddy currents within the metallic material.
[0030] In one embodiment, the first and second activation sequences
are identical.
[0031] In one embodiment, said selectively activating comprises
sequentially activating groups of probe elements at different ones
of the time-spaced instances, each group of probe elements
comprising at least one probe element for which the transmitter
coil is activated and the receiver is activated, an identification
of the at least one probe element varying from one of the
time-spaced instances to another one of the time-spaced
instances.
[0032] In one embodiment, the at least one probe element comprises
at least two probe elements, two following ones of the at least two
probe elements being spaced apart by an inactive probe element at
each one of the time-spaced instances.
[0033] In another embodiment, said selectively activating comprises
sequentially activating groups of probe elements at different ones
of the time-spaced instances, each group of probe elements
comprising at least one set of at least three adjacent probes, the
receiver of each one of the at least three adjacent probes being
activated and the transmitter coil of a central one of at least the
three adjacent probes being activated concurrently with the
activation of the receiver.
[0034] In one embodiment, the at least one set of at least three
adjacent probe elements comprises a first set of at least three
probe elements and a second set of at least three probe elements,
the first and second sets being spaced apart by at least one
inactive probe element at each one of the time-spaced
instances.
[0035] In a further embodiment, said selectively activating
comprises sequentially activating groups of probe elements at
different ones of the time-spaced instances, each group of probe
elements comprising at least one set of at least three adjacent
probes, the transmitter coil of each one of the at least three
adjacent probes being activated and the receiver of a central one
of at least the three adjacent probes being activated concurrently
with the activation of the receiver.
[0036] In one embodiment, the at least one set of at least three
adjacent probe elements comprises a first set of at least three
probe elements and a second set of at least three probe elements,
the first and second sets being spaced apart by at least one
inactive probe element at each one of the time-spaced
instances.
[0037] In one embodiment, the metallic material comprises a
non-metallic surface coating.
[0038] In one embodiment, the step of moving is performed
substantially continuously.
SHORT DESCRIPTION OF THE DRAWINGS
[0039] Further features and advantages of the present invention
will become apparent from the following detailed description, taken
in combination with the appended drawings, in which:
[0040] FIG. 1 illustrates a probe element positioned adjacent to a
surface to be inspected, in accordance with an embodiment;
[0041] FIG. 2a illustrates a probe element comprising a receiver
coil mounted on a transmitter coil, in accordance with an
embodiment;
[0042] FIG. 2b illustrates a probe element comprising a receiver
coil mounted spaced apart from a transmitter coil, in accordance
with an embodiment;
[0043] FIG. 3 illustrates a probe element comprising a transmitter
coil mounted on a cylindrical core and a receiver coil mounted on
the transmitter coil, in accordance with an embodiment;
[0044] FIG. 4 illustrates a probe element comprising a transmitter
coil mounted on a core having two legs and a receiver coil mounted
on the transmitter coil, in accordance with an embodiment;
[0045] FIGS. 5a-5b illustrate the generation by the probe element
of FIG. 4 of a magnetic field and an eddy current within a material
to be inspected, in accordance with an embodiment;
[0046] FIG. 6 illustrates the positioning of the probe element of
FIG. 4 relative to a material having a surface-braking defect, in
accordance with an embodiment;
[0047] FIG. 7 illustrates the probe element of FIG. 4 encapsulated
in a casing, in accordance with an embodiment;
[0048] FIG. 8 illustrates an array probe comprising nine probe
elements and positioned on a flat surface, in accordance with an
embodiment;
[0049] FIG. 9 illustrates an array probe comprising nine
spring-loaded probe elements and positioned on an irregular
surface, in accordance with an embodiment;
[0050] FIG. 10 illustrates a complex voltage plane representation
comprising a single defect response, in accordance with an
embodiment;
[0051] FIG. 11 illustrates a complex voltage plane representation
comprising three same defect responses positioned at different
lift-off positions, in accordance with an embodiment;
[0052] FIG. 12 illustrates a complex voltage plane representation
comprising three different defect responses positioned at a same
different lift-off position, in accordance with an embodiment;
[0053] FIG. 13 illustrates a probe element comprising the probe
element of FIG. 4 and a pancake coil, in accordance with an
embodiment;
[0054] FIGS. 14a and 14b illustrate a transmitter coil and a
pancake coil arranged in different relative positons, in accordance
with an embodiment;
[0055] FIG. 15a is a top view of eddy current propagating in a
material to be inspected provided with a surface-breaking defect,
in accordance with an embodiment;
[0056] FIG. 15b illustrates the probe element of FIG. 13 positioned
at the two ends of the surface-braking defect extending along the
material of FIG. 15a, in accordance with an embodiment;
[0057] FIG. 15c illustrates the voltage response of the pancake
coil of the probe element of FIG. 15b as a function of the position
of the probe element along the material to be inspected, in
accordance with an embodiment;
[0058] FIG. 16 illustrates the probe element of FIG. 13
encapsulated in a casing, in accordance with an embodiment;
[0059] FIG. 17 illustrates three pancake coils arranged in a linear
configuration, in accordance with an embodiment;
[0060] FIG. 18a illustrates an array probe comprising eleven probe
elements of which the first, fifth, and ninth probe elements are
active, in accordance with an embodiment;
[0061] FIG. 18b illustrate the array probe of FIG. 18a of which the
second, sixth, and tenth probe elements are active, in accordance
with an embodiment;
[0062] FIG. 19a illustrates the array probe of FIG. 18a in which
the transmitter coil of the first, second, third, eight, ninth, and
tenth probe elements is active and the receiver coils of the second
and ninth probe elements are active, in accordance with an
embodiment;
[0063] FIG. 19b illustrates the array probe of FIG. 18a in which
the transmitter coil of the second, third, fourth, ninth, tenth,
eleventh probe elements is active and the receiver coils of the
third and tenth probe elements are active, in accordance with an
embodiment;
[0064] FIG. 20a illustrates the array probe of FIG. 18a in which
the transmitter coil of the second, sixth, and tenth probe elements
is active and the receiver coils of the first, second, third,
fifth, sixth, seventh, ninth, tenth, and eleventh probe elements
are active, in accordance with an embodiment;
[0065] FIG. 20b illustrates the array probe of FIG. 18a in which
the transmitter coil of the third, seventh, and eleventh probe
elements is active and the receiver coils of the second, third,
fourth, sixth, seventh, eighth, tenth, and eleventh probe elements
are active, in accordance with an embodiment;
[0066] FIG. 21 illustrates two array probes being transversally
shifted;
[0067] FIG. 22 illustrates a core comprising a central cylindrical
section having a first transmitter coil mounted thereto, a first
leg extending from a first end of the central section and having a
second transmitter coil mounted thereto, and a second leg extending
from a second end of the central section and having a third
transmitter coil mounted thereto, in accordance with an
embodiment;
[0068] FIG. 23 illustrates a core comprising a central cylindrical
section, a first leg extending from a first end of the central
section and having a first transmitter coil mounted thereto, and a
second leg extending from a second end of the central section and
having a second transmitter coil mounted thereto, in accordance
with an embodiment;
[0069] FIG. 24 illustrates a curved core having a single
transmitter coil mounted thereto, in accordance with an
embodiment;
[0070] FIG. 25 illustrates a curved core having three transmitter
coils mounted thereto, in accordance with an embodiment;
[0071] FIG. 26 illustrates a prism having a single transmitter coil
mounted thereto, in accordance with an embodiment;
[0072] FIG. 27 illustrates a prism having three transmitter coils
mounted thereto, in accordance with an embodiment;
[0073] FIG. 28 illustrates a distribution of eddy current density
obtained within a material when a single probe element is used to
generate a magnetic field, in accordance with an embodiment;
[0074] FIG. 29 illustrates a distribution of eddy current density
obtained within a material when an array probe comprising three
probe elements is used to generate a magnetic field, in accordance
with an embodiment;
[0075] FIG. 30 illustrates a distribution of eddy current density
obtained within a material when a single, large transmitter is used
to generate a magnetic field within a material to be inspected, in
accordance with the prior art; and
[0076] FIG. 31 illustrates a distribution of eddy current density
obtained within the material of FIG. 30 when an array probe
comprising five probe elements is used to generate a magnetic
field, in accordance with an embodiment.
[0077] It will be noted that throughout the appended drawings, like
features are identified by like reference numerals.
DETAILED DESCRIPTION
[0078] There is described an eddy current array probe having a
probe body which includes at least two independent probe elements.
Each probe element is composed of at least one coil which acts as
an emitter and a receiver. Alternatively, the probe element may
comprise at least one transmitter and at least one receiver. The
probe elements are arranged in a linear configuration. They are
therefore provided side-by-side, along a transversal dimension of
the probe body, orthogonal to a scan direction when the eddy
current array probe is in use. The probe elements can be
longitudinally aligned or misaligned with respect to one another.
They can be provided on a single row of coil elements or on a
plurality of transversal rows. The rows can be transversally
aligned or misaligned within the probe body.
[0079] A pair of transmitter-receiver of one probe element is used
for the detection and depth sizing of longitudinally oriented
surface-breaking defects in a metallic material. In addition to the
selected pair, additional individual transmitters and/or receivers
from other neighboring elements are also used.
[0080] FIG. 1 illustrates one embodiment of a probe element 10. The
probe element 10 extends along a longitudinal axis and comprises at
least one transmitter adapted to generate a magnetic field and a
receiver adapted to detect a magnetic field. When in use, the probe
element 10 is positioned so as to be substantially parallel to a
surface 12 of a piece of metallic material 14 to be inspected, i.e.
the longitudinal axis of the probe element 10 is substantially
parallel to the surface 12. When in use, the probe element 10 is
moved relative to the surface 12 along a scanning direction 16 so
that the longitudinal axis of the probe element 10 is parallel to
the surface 12 of the material being examined 14 and parallel to
the scanning axis 16. If a surface-breaking defect extends in the
material to be examined 14 along the scanning direction 16, the
probe element 10 will detect the defect and size the depth of the
defect.
[0081] It should be understood that the probe element 10 may be
contained within a probe casing or body. The probe casing comprises
a scanning surface which is sized and shaped so as to be placed on
the surface 12 of the material to be examined 14 and moved along
the surface 12. The position of the probe element 10 within the
probe casing is chosen so that the magnetic field generated by the
transmitter of the probe element 10 may propagate within the
material to be examined 14, thereby inducing an eddy current within
the material to be examined 14, and the receiver of the probe
element 10 may detect a magnetic field induced by the eddy current
within the material 14 when the scanning surface of the casing is
positioned on the surface 12 of the material 14.
[0082] It should also be understood that the transmitter is
electrically connected to a current source such as an alternate
current (AC) source. When an AC current having an operation
frequency propagates though the transmitter, the transmitter
generates a first magnetic field of which a portion penetrates the
material to be examined 14. As a result of the first magnetic field
generated by the transmitter, eddy currents are induced in the
material 14. The eddy currents in turn induce a second magnetic
field. The receiver of the probe element 10 is electrically
connected to a voltage sensor adapted to measure the induced
voltage in the receiver. The receiver is adapted to sense a portion
of the magnetic field induced by the eddy current, i.e. the second
magnetic field generated by the eddy current induces an electrical
voltage within the receiver and the voltage sensor measures the
induced voltage at the terminals of the receiver. As a result, when
the flow of eddy current induced within the material is modified
due to the presence of a surface-breaking defect, the magnetic
field induced by the eddy current is modified, which in turn
modifies the voltage measured by the voltage sensor. The voltage
variations measured at the terminals of the receiver are then
indicative of the variations of eddy current deflected by the
defect.
[0083] FIG. 2a illustrates an exemplary probe element 20 which
comprises a transmitter coil 22 and a receiver coil 24. The
transmitter coil 22 extends along a longitudinal axis 26 and is
provided with given internal and external diameters and a given
length along the longitudinal axis 26. The receiver coil 24 also
extends along the longitudinal axis 26 so that the transmitter coil
22 and the receiver coil 24 are concentric and coaxial. The
receiver coil 24 is provided with given internal and external
diameters and a given length along the longitudinal axis 26. The
receiver coil 24 is mounted on the transmitter coil 22, i.e. the
internal diameter of the receiver coil 24 is substantially equal to
the external diameter of the transmitter coil 22.
[0084] It should be understood that the receiver coil 24 could be
independent from the transmitter coil 22 while still being
concentric and coaxial with the transmitter coil 22. In this case,
the internal diameter of the receiver coil 24 may be different from
the external diameter of the transmitter coil 22.
[0085] FIG. 2b illustrates an exemplary probe element 30 which
comprises a transmitter coil 32 and a receiver coil 34 which is
positioned away from the transmitter coil 32 so that the
transmitter and receiver coils 32 and 34 are not in physical
contact. In the illustrated embodiment, the longitudinal axis of
the transmitter coil 32 is parallel to that of the receiver coil
34. It should be understood that the distance between the
transmitter and receiver coils 32 and 34 and the relative position
between the transmitter and receiver coils 32 and 34 are chosen so
that the receiver coil 34 may detect the eddy current generated by
the transmitter coil 32. In one embodiment, the receiver coil 32 is
to be positioned as close as possible from the surface to be
inspected.
[0086] While in FIGS. 2a and 2b, it is shorter than the transmitter
coil 22, 32, it should be understood that the receiver coil 24, 34
may have substantially the same length as the transmitter coil 22,
32 or be longer than the transmitter coil 22, 32.
[0087] In one embodiment, the diameter of the transmitter coil 22,
32 and the diameter of the receiver coil 24, 34 are chosen as a
function of a desired measurement sensitivity, knowing that
decreasing the diameter of the transmitter coil and/or the receiver
coil increases the sensitivity.
[0088] FIG. 3 illustrates a further example of a probe element 40
which comprises a transmitter coil 42 and a receiver coil 44
mounted on the transmitter coil 42. The probe element 40 further
comprises a cylindrical core 46 on which the transmitter coil 42 is
assembled. The core 46 allows increasing the amplitude of the
magnetic field generated by the transmitter coil 42.
[0089] In one embodiment, the core 46 is made of a material having
a high magnetic permeability. In one embodiment, the material from
which the core 46 is made further has a low electrical
conductivity. In one embodiment the core 46 is made of ferrite or
ferritic steel.
[0090] FIG. 4 illustrates one embodiment of a probe element 50
which comprises a core 52 such as a ferrite core or ferritic steel
core. The core 52 comprises a central cylinder 54 and a pair of
cylindrical legs 56 which each extends from the cylinder 54 at a
respective end thereof. Each leg 56 is provided with a surface
contacting end 58 which may be adapted to be positioned on the
surface 12 of the material to be inspected 14. The probe element 50
further comprises a transmitter coil 60 assembled on the central
cylinder 54 of the core 52, and a receiver coil 62 mounted on the
transmitter coil 60. The legs 56 allows better guiding the magnetic
field generated by the transmitter coil 60 and enhancing the
magnetic coupling with the material to be inspected 14 with respect
to the probe element 40 for example.
[0091] While they are cylindrical, it should be understood that the
core 52 and the legs 56 illustrated in FIG. 4 may have different
shape. For example, the legs 56 may have a square or rectangular
cross-sectional shape.
[0092] FIGS. 5a-5b illustrates the operation of the probe element
50. The probe element is positioned relative to the surface 12 of
the material to be inspected 14 so that the ends 58 be adjacent to
the surface 12. An AC current is propagated through the transmitter
coil 60, and as a result of the AC current, a magnetic field 64 is
generated between the legs 56 of the core 52. A portion of the
generated magnetic field extends within the material 14, as
illustrated in
[0093] FIG. 5b which shows a cross-sectional view of the material
14.
[0094] The portion of the magnetic field 64 that extends within the
material 14 generates an eddy current illustrated by arrows 66
within the material 14. The direction of the eddy current 66 is
orthogonal to the magnetic field 64, and is therefore orthogonal to
the longitudinal axis of the transmitter coil 60. It should be
understood that the direction of the eddy current periodically
changes from the direction illustrated by arrow 66 to an opposite
direction as the flow of electric charge of the AC current
periodically reverses direction. The eddy current 66 induces a
magnetic field which in turn induces an electrical voltage within
the receiver coil 62.
[0095] FIG. 6 illustrates the detection of a defect by the probe
element 50. The probe element is positioned adjacent to or in
contact with a surface 70 of a material 72 to be inspected that
comprises a longitudinal defect 74 such as a surface-breaking
crack. The longitudinal defect extends at least partially along a
longitudinal axis. The probe element 50 is positioned so that the
axis between the legs 56 of the core 52 substantially corresponds
to the longitudinal axis of the defect 74, i.e. the legs 56 are
positioned so as to lie on the defect 74. In this case, the eddy
current 76 generated by the transmitter coil 60 within the material
72 is substantially orthogonal to the defect 74 and the flow of
eddy current 76 is modified by the defect 74. As a result, the
induced voltage at the receiver coil 62 changes, and the presence
and depth of the defect 74 can be detected from the variation of
the induced voltage.
[0096] FIG. 7 illustrates one embodiment of a probe assembly 78
that comprises a probe casing 80 adapted to protect the probe
element 50 and in which the probe element 50 is packaged. The
casing 80 comprises a surface contacting face 82 having an internal
surface 84 and an external surface 86 adapted to be in physical
contact with the surface of the material to be inspected. The probe
element 50 is secured within the casing 80 so that the legs 56 of
the core 52 be secured to the internal surface 84 of the surface
contacting face 82. The external surface 86 of the surface
contacting face 82 is curved so as to accommodate physical
irregularities that may be present on the surface to be
inspected.
[0097] It should be understood that the external surface 86 of the
surface contacting face 82 may be provided with any other adequate
shape. For example, the external surface 86 may be substantially
planar. In another embodiment, the external surface 86 may comprise
a planar central section sandwiched between beveled ends.
[0098] While the casing 80 has a rectangular cross-sectional shape,
it should be understood that any other adequate shape may be
used.
[0099] In one embodiment, at least the surface-contacting face 82
of the casing 80 is made of a flexible material in order to
accommodate physical irregularities that may be present on the
surface to be inspected.
[0100] FIG. 8 illustrates one embodiment of an array probe 90 that
comprises nine probe assemblies 92-108 which may all correspond to
the probe assembly 78. Each probe assembly 92-108 comprises a core
provided with two legs, such as core 52, a transmitter coil, and a
receiver coil. The probe assemblies 92-108 are arranged in a linear
configuration, i.e. they are positioned side-by-side along a
transversal axis which is parallel to the direction of the flow of
the eddy currents generated by the transmitter coils and orthogonal
to a scan direction, when the array probe 90 is in use. In this
configuration, the axes between the legs of each probe element
92-108 are all parallel to each other so that the flows of eddy
currents generated by the probe elements 92-108 are also all
parallel to each other.
[0101] While the array probe 90 comprises nine probe assemblies, it
should be understood that the number of probe elements or probe
assemblies contained in an array probe may vary as long as the
array probe comprises at least two probe elements or probe
assemblies.
[0102] In FIG. 8, the array probe 90 is positioned on a surface 110
of a material to be inspected 112. The material 112 comprises three
surface-breaking defects 114-118 and the array probe 90 is
positioned so that the probe assemblies 92, 96, and 106 are
positioned on top of the defects 114, 116, and 118, respectively.
Therefore, the eddy currents flowing below the probe assemblies 92,
96, and 106 will be different from the eddy currents flowing below
the probe assemblies 94, 98-102, and 106, which allows determining
that a defect is present under the probe assemblies 92, 96, and
106.
[0103] The probe assemblies 92-108 are selectively operated over
time, i.e. groups of at least one probe assemblies 92-108 are
sequentially operated, as described in further detail below.
[0104] It should be understood that the number of probe assemblies
may vary as along as the array probe comprises at least two probe
assemblies. The relative positioning of the probe assemblies 92-108
may also vary. While in FIG. 8 the probe assemblies 92-108 are all
parallel to generate parallel flows of eddy currents, it should be
understood that other configuration may be possible. For example,
an array probe may comprise two probe assemblies that are
positioned at a 45 degrees angle so that the angle between the
flows of generated eddy currents be 45 degrees.
[0105] FIG. 9 illustrates one embodiment of a spring-loaded array
probe 120 which comprises nine probe assemblies 92-108. The
spring-loaded array probe 120 further comprises a frame 122 to
which the probe assemblies 92-108 are each movably secured to the
frame 122 via a respective spring 124 to accommodate variations of
the surface 126 of a material to be inspected 128 and minimize the
distance between the probe assemblies 92-108 and the surface to be
inspected 126.
[0106] In the illustrated embodiment, the spring-loaded array probe
120 is positioned so that the probe assemblies 92, 94, 106, and 108
are in physical contact with the planar section of the surface to
be inspected 126 while the probe assemblies 96-102 are in physical
contact a weld crown 130 which forms a protrusion that extends from
the surface 126. The spring connected to the probe assemblies
96-102 are compressed while the springs connected to the probe
assemblies 92, 94, 106, and 108 are in an extension position.
[0107] It should be understood that any adequate device for
spring-loading the probe assemblies 92-108 may be used. For
example, the springs 124 may be replaced by memory foam.
[0108] As described above, the voltage is measured at the terminals
of the receiver coil of a probe element or a probe assembly. FIG.
10 illustrates the determined voltage when represented in a complex
voltage plane. For a given excitation frequency, the positioning of
the receiver coil relative to the eddy current induced by the
transmitter coil, i.e. having the longitudinal axis of the receiver
coil substantially orthogonal to the flow of eddy current and
substantially parallel to the surface to be inspected, allows
obtaining orthogonality between a defect response 130 indicative of
the depth of a defect and the lift-off signal 132. This particular
positioning of the receiver coil allows measuring independently and
concurrently lift-off variations (along a horizontal axis) and
amplitude variations originating from a defect response (along a
vertical axis). Depending on characteristics such as the operation
frequency, the dimensions of the transmitter/receiver, the
materials of the transmitter and receiver, and/or the like, the
angle between the defect response 130 and the lift-off response 132
within the complex voltage plane may vary from 90 degrees, while
the defect and lift-off response may still be considered as being
orthogonal for the purpose of the present description. For example,
an angle of about 125 degrees may be formed between the defect and
lift-off responses 130 and 132 and the defect and lift-off
responses may still be considered as being orthogonal.
[0109] FIG. 11 illustrates the voltage variation caused by a same
defect and represented in a complex voltage plane when the distance
between the receiver coil and the surface to be inspected varies.
As illustrated in FIG. 11, increasing the distance between the
receiver coil and the surface to be inspected shifts the defect
response towards greater values of lift-off response. For example,
the defect response 140a corresponding to a zero lift-off response
represents the case where the receiver coil is in physical contact
with the surface to be inspected. If the distance between the
receiver coil and the surface to be inspected is increased, e.g. if
a 1 mm layer of coating or painting is located between the receiver
coil and the surface, the defect response shifts toward a greater
value of lift-off response, as illustrated by defect response 140b.
If the distance between the receiver coil and the surface to be
inspected is further increased, e.g. if a 2 mm layer of coating or
painting is located between the receiver coil and the surface, the
defect response shifts toward an even greater value of lift-off
response, as illustrated by defect response 140c. It should also be
noted that the maximal amplitude of the defect response decreases
as the distance between the receiver coil and the surface to be
inspected increases.
[0110] In one embodiment, using calibration, it is possible to
compensate for the energy losses caused by lift-off between the
probe and the surface by applying a predetermined compensation gain
to the maximal amplitude of the defect response, and thereby
determine the correct defect depth even if the defect is located
below a layer of coating or painting for example.
[0111] FIG. 12 illustrates the voltage variation caused by
different defects and represented in a complex voltage plane when
the different defects have a different depth. As illustrated in
FIG. 12 and for a same distance between the receiver coil and the
surface to be inspected, increasing the depth of a defect increases
the amplitude of the defect response. For example, the defect
response 144a having a first maximal amplitude represents the case
where the sensed defect has a first depth.
[0112] If the depth of the defect is increased up to a second depth
which is greater than the first depth, the maximal amplitude of the
defect increases up to a second maximal value, as illustrated by
defect response 144b. If the depth of the defect is further
increased up to a third depth which is greater than the second
depth, the maximal amplitude of the defect increases up to a third
maximal value, as illustrated by defect response 144c. The greater
the depth of a defect is, the more the eddy current is deflected by
the defect and the less energy is coupled into the receiver
coil.
[0113] FIG. 13 illustrates a further example of a probe element 150
which comprises the probe element 50 and a further receiver coil
152 such as a pancake coil. The probe element 150 may be used for
determining the length of a defect while the probe element 150 is
moved along a defect present in the material 14. The receiver coil
152 extends along a longitudinal axis that is orthogonal to the
longitudinal axis of the receiver coil 62 and also orthogonal to
the surface 12 when the probe element 150 scans the surface 12.
[0114] While the receiver coil 62 is adapted to sense eddy currents
that are deflected by the defect in a plane that is substantially
orthogonal to the surface to be inspected 12 since the longitudinal
axis of the receiver coil 62 is substantially orthogonal to the
flow of eddy current and substantially parallel to the surface to
be inspected 12, the receiver coil 152 is adapted to sense eddy
currents that swirl around defect ends and are deflected in a plane
that is substantially parallel to the surface to be inspected 12,
as illustrated in FIG. 15a, since the longitudinal axis of the
receiver coil 152 is substantially orthogonal to the surface to be
inspected 12.
[0115] FIGS. 14a and 14b illustrate different relative positons
between a transmitter coil 154 and a receiver coil 152. As
illustrated in FIG. 14a, the receiver coil 152 may be in physical
contact with the transmitter coil 154 as long as its longitudinal
axis is orthogonal to the surface to be inspected and to the flow
of induced eddy current. As illustrated in FIG. 14b, the receiver
coil 152 may be independent from the transmitter coil 154 so that
the two coils are not in physical contact together, as long as its
longitudinal axis is orthogonal to the surface to be inspected and
to the flow of induced eddy current.
[0116] FIG. 15b illustrates the probe element 150 at two different
positons relative to a defect 160 extending longitudinally within a
material to be inspected 162 between a first end 164 and a second
end 166. The probe element 150 is positioned on the surface 168 of
the material to be inspected 162 so that the longitudinal axes of
the transmitter and receiver coils 60 and 62 are collinear with the
longitudinal axis of the defect 160. The probe element 150 is moved
on the surface 168 along a scan direction which is collinear with
the longitudinal axis of the defect 160. As illustrated in FIG. 15a
which shows the top view of the eddy current while the probe
element 150 moves along the defect 160, the eddy current swirls and
gets around each end 164 and 166 in a plane that is parallel to the
surface 168 while is cut by the defect 160 or the eddy current
propagates under the defect 160 between the two ends 164 and 166. A
deflection of the eddy current induced by the transmitter coil 60
within a plane that is parallel to the surface 168 is detected by
the receiver coil 152.
[0117] When no defect is present in the material, the voltage 170
of the receiver coil 152 is substantially constant, as illustrated
in FIG. 15c. When the probe element 150 reaches the position 150a,
the coil receiver 152 is located on top of the first end 164 of the
defect 160 and the first end deflects the eddy current 176 within a
plane parallel to the surface 168 according to a first direction,
e.g. the anti-clockwise direction. The deflection of the eddy
current 176 by the first end 164 of the defect 160 induces a
variation of the voltage 170 which reaches a maximum 172. Once the
receiver coil 152 has passed over the first end 162 of the defect
160, the eddy current 180 is cut by the defect 160 or propagates
under the defect in a plane orthogonal to the surface 168 and the
voltage 170 comes back to its initial value. When the probe element
150 reaches the position 150b, the coil receiver 152 is located on
top of the second end 166 of the defect 160 and the second end 166
deflects the eddy current 178 within a plane parallel to the
surface 168 according to a second direction, e.g. the clockwise
direction. The deflection of the eddy current 178 by the second end
166 of the defect 160 induces a variation of the voltage 170 which
reaches a minimum 172. The length L of the defect 160 can therefore
be determined by measuring the distance covered by the receiver
coil 152 or the probe element 150 between the detection of the
voltage maximum 172 and the detection of the voltage minimum
174.
[0118] While in FIG. 15, the beginning 164 of the defect 160
corresponds to a voltage maximum 172 and the end 166 of the defect
160 corresponds to a voltage minimum 174, it should be understood
that the contrary may be possible, i.e. a voltage minimum may
correspond to the beginning of the defect 160 and a voltage maximum
may correspond to the end of the defect.
[0119] FIG. 16 illustrates a probe assembly 180 which comprises the
probe element 150 which includes the probe element 50 and the
receiver coil 152. As for the coil assembly 78 illustrated in FIG.
7, the probe assembly 180 comprises a casing 80 in which the probe
element 150 is packaged. The casing 80 comprises a surface
contacting face 82 having an internal surface 84 and an external
surface 86 adapted to be in physical contact with the surface of
the material to be inspected. The probe element 50 is secured
within the casing 80 so that the legs 56 of the core 52 be secured
to the internal surface 84 of the surface contacting face 82. The
receiver coil 152 is secured to the internal surface 84 of the
surface contacting face 82 between the legs 56 of the core 52. The
external surface 86 of the surface contacting face 82 is curved so
as to accommodate physical irregularities that may be present on
the surface to be inspected.
[0120] When an array probe comprises at least two probe elements
150 or probe assemblies 180, the receiver coils 152 may also be
used for detecting transverse defects. FIG. 17 schematically
illustrates three receiver coils 152a-152c such as three pancake
coils which each belong to a respective probe element 150 or probe
assembly 180. In one embodiment, the coil 152b is used as a
transmitter for generating a magnetic field and at least one of its
neighbor coils 152a and 152c is used as a receiver for detecting
the eddy current induced by the coil 152b. Such a configuration is
referred to as "short transmit-received" configuration. A
transverse defect may then be detected from the voltage variation
within the coil 152a and/or 152c. In another embodiment, the coil
152a is used as a transmitter for generating a magnetic field and
its second neighbor coil which is not adjacent thereto, i.e. coil
152c, is used as a receiver for sensing the eddy current induced by
the coil 152a. Such a configuration is referred to as a "long
transmit-receive" configuration. A transverse defect may then be
detected from the voltage variation within the coil 152c.
[0121] FIGS. 18a and 18b illustrates an exemplary probe array 200
which comprises eleven probe assemblies 202-222. While in the
illustrated embodiment, each probe assembly 202-222 corresponds to
the probe assembly 180, it should be understood that each probe
assembly 202-222 may each correspond to the probe assembly 78. It
should also be understood that the number of probe elements or
assemblies contained in the array probe 200 may vary as long as the
array probe 200 comprises at least two probe elements 78 or 150 or
probe assemblies 180. When the array probe 200 comprises at least
one probe assembly 180, it should be understood that the receiver
coil 152 may be omitted from the probe assembly 180.
[0122] When the array probe 200 is in operation or use, the probe
elements or assemblies contained in the array probe 200 are
selectively activated at different instances of time, i.e. the
probe elements or assemblies are divided into active elements and
inactive elements at each instance of time. An active element is
defined as a probe element or probe assembly of which the
respective transmitter coil is excited to generate a magnetic field
and/or the receiver coil is used to detect an eddy current. An
inactive element is defined as a probe element or assembly of which
the transmitter coil is not excited, and therefore does not
generate a magnetic field, and of which the receiver coil is not
used to detect an eddy current.
[0123] Active elements and inactive elements vary in time, i.e. the
identification of the active elements and the identification of the
inactive elements change from one instance of time to another. In
one embodiment, a given probe element or assembly that is active at
a given time instance cannot be active at another time instance as
long as all of the probe elements or assemblies have not been
activated. In another embodiment, a given probe element or assembly
that has been activated at a given instance of time can be
activated at a subsequent instance of time even if not all of the
other probe elements or assemblies have been activated between the
given and subsequent instances of time.
[0124] In one embodiment, the probe elements or assemblies are
activated according to an activation sequence. The activation
sequence comprises a sequence of instances of time and a respective
identification of active and inactive elements for each instance of
time contained in the sequence of time instances. As a result, for
a first instance of time, the probe elements or assemblies of a
first group are activated while the other probe elements or
assemblies are inactive. At a second instance of time that is
spaced in time from the first instance of time, the probe elements
or assemblies of a second group are activated while the other probe
elements or assemblies are inactive, etc. It should be understood
that at least one probe element or assembly may not be activated
during an activation sequence. For example, while the array probe
200 comprises nine probe elements or assemblies, only seven of the
probe elements or assemblies may be used to scan a surface to be
inspected.
[0125] Once the activation sequence has been completed, the array
probe may be moved relative to the surface to be inspected at a
different positon relative to the surface along a scan direction.
Once the array probe 200 has been positioned at the new position
relative to the surface to be inspected, the probe elements or
assemblies are activated according to the same activation sequence
or another activation sequence.
[0126] It should be understood that each transmitter coil 60
contained in the array probe 200 is connected to an AC power source
for propagating an electrical current therein and thereby
generating a magnetic field. Similarly, each receiver coil 62
and/or 152 is connected to a voltage sensor for measuring the
voltage between the terminals of the receiver coil 62, 152. It
should be understood that a same power source may be used
selectively activate the transmitter coils 60 and a same voltage
sensor may be used to selectively measure the voltages at the
receiver coils 62, 152. A controller is used to control the power
source(s) and the voltage sensor(s) according to the activations
sequence. In one embodiment, the controller comprises at least a
processing unit, a storing unit, and a communication unit for
sending control signals to the power source(s) and the voltage
sensor(s). The activation sequence is stored in the storing unit.
The processing unit is adapted to retrieve the activation sequence
from the storing unit and control the probe elements or assemblies
according to the retrieved activation sequence. Using the
activation sequence, the processing unit identifies, for each
instance of time, the probe elements or assemblies for which their
respective transmission coil is to be activated and the probe
elements or assemblies for which the voltage of the receiver coil
is to be read. For each instance of time, the processing unit send,
via the communication unit, an activation signal indicative of the
identification of the transmission coils to be activated to the
power source(s) and an activation signal indicative of the
identification of the receiver coils for which the voltage is to be
determined to the voltage sensor.
[0127] In an embodiment in which each transmitter coil is connected
to a respective AC power source, the processing unit may send an
activation signal to each power source connected to an identified
transmitter coil. In this case, the power sources that receive an
activation signal activates their respective transmitter coil. In
an embodiment in which a single power is used to control all of the
transmitter coils, the processing unit is adapted to send an
activation signal that identifies the given transmitter coils to be
activated. In this case, the power source only activates the
transmitter coils that are identified in the received activation
signal.
[0128] In an embodiment in which each receiver coil is connected to
a respective voltage sensor, the processing unit may be adapted to
send a respective activation signal to each voltage sensor
connected to an identified receiver coil. In this case, each
voltage sensor that receives an activation signal from the
controller measures the voltage at the terminals of its respective
receiver coil. In an embodiment in which a single voltage sensor is
used for measuring the voltage of all of the receiver coils, the
processing unit is adapted to send to the voltage sensor an
activation signal that comprises an identification of the receiver
coils for which the voltage is to be measured. In this case, the
voltage sensor measures only the voltage of the identified receiver
coils.
[0129] In one embodiment, the controller or an acquisition unit is
adapted to receive voltage measurements from the voltage sensor(s)
and store the received voltage measurement. The controller or
acquisition unit may then identify the presence of a defect and
determine the depth of the identified defect. The processing unit
of the controller or acquisition unit is then adapted to receive
the voltage values and determine the corresponding voltage of each
corresponding AC operation frequencies. In one embodiment, the
processing unit is adapted to create and store a complex voltage
plane representation, and optionally display this representation on
a display unit. In one embodiment, the processing unit is adapted
to apply a compensation gain to the defect response of the complex
voltage plane representation.
[0130] While the probe elements or assemblies contained in the
array probe 200 are all parallel, i.e. the longitudinal axes of the
transmitter coils of all of the probe elements or assemblies are
all parallel, it should be understood that other configuration may
be possible. For example, at least two probe elements or assemblies
may have different orientations to detect defects extending along
different longitudinal axes. For example, the transmitter coil of a
first probe element or assembly may extends along a first
longitudinal axis and the transmitter coil of a second probe
element or assembly may extends along a second longitudinal axis
which is not parallel to the first longitudinal axis.
[0131] Referring back to FIGS. 18a and 18b, the probe assemblies
202-222 are multiplexed using the following method in order to
minimize mutual inductance between adjacent coils. At a first point
in time, a first group of non-adjacent probe assemblies 202-222 is
excited. For example, the first group may comprise the probe
assemblies 202, 210, and 218 so that three inactive probe
assemblies are present between two active or excited probe
assemblies, as illustrated in FIG. 18a. The transmitter coils 60 of
the probe assemblies 202, 210, and 218 are excited substantially
concurrently to generate a respective magnetic field. The magnetic
field generated by each probe assembly 202, 210, and 218 induces a
respective eddy current which is detected by the respective
receiver coil 62 of the probe assembly 202, 210, and 218. Once the
receiver coils 62 have sensed the eddy currents, the probe
assemblies 202, 210, and 218 are deactivated and a second group of
non-adjacent probe assemblies 202-222 is excited or activated at a
second instance of time. For example, the second group of
non-adjacent probe assemblies may contain the first right neighbor
of each probe assemblies 202, 210, and 218, i.e. probe assemblies
204, 212, and 220, as illustrated in FIG. 18b. The transmitter
coils 60 of the probe assemblies 204, 212, and 220 are then excited
substantially concurrently to generate a respective magnetic field.
The magnetic field generated by each probe assembly 204, 212, and
220 induces a respective eddy current which is detected by the
respective receiver coil 62 of the probe assembly 204, 212, and
220. Once the receiver coils 62 have sensed the eddy currents, the
probe assemblies 204, 212, and 220 are deactivated. At a subsequent
third instance of time, a third group of non-adjacent probe
assemblies, e.g. probe assemblies 206, 214, and 222, is excited,
etc. Once all of the probe assemblies 202-222 have been selectively
excited, the array probe 200 is moved up to a second positon in a
scan direction which is parallel to the longitudinal axes of the
transmitter and receiver coils 60 and 62. Once the array probe has
been moved to the second position, the first group of probe
assemblies, the second group, the third group, etc. are selectively
excited and measurements are performed. Then the array probe is
moved to a third position along the scan direction and the probe
assemblies are selectively excited according to the above-described
group distribution, etc. It should be understood that several
defects extending along substantially parallel axes may be scanned
using the array probe 200.
[0132] In one embodiment, the displacement of the array probe 200
is performed in a stepwise manner. In another embodiment, the
displacement of the array probe along the surface is
continuous.
[0133] While in the present embodiment three inactive or
non-excited probe assemblies are inserted between two following
excited probe assemblies, it should be understood that other
configurations may be possible as long as at least one non-excited
probe assembly is located between two excited probe assemblies at
each point in time. For example, two excited probe assemblies could
be spaced apart by two non-excited probe assemblies. In one
embodiment, the number of inactive probe assemblies positioned
between two active assemblies is chosen so as to reduce or
eliminate crosstalk between the active probe assemblies.
[0134] In one embodiment, the receiver coil 152 of each excited
probe assembly 202-222 further detects its respective eddy current
in order to measure the length of a longitudinal defect using the
above-described method.
[0135] In one embodiment, selectively operating the probe
assemblies 202-222 according the operation method illustrated in
FIGS. 18a and 18b allows covering a large surface while minimizing
parasitic signals that would come from adjacent coils rather than
the material being inspected.
[0136] In one embodiment, multiplexing several relatively small
probe assemblies allows obtaining an increased resolution compared
to having a single, large transmitter for example.
[0137] While in the operation mode of the array probe 200
illustrated in FIGS. 18a and 18b the eddy currents are each
generated by a single transmitter coil, it should be understood
that at least two neighbor transmitter coils may be concurrently
excited to generate an eddy current. The neighbor transmitter coils
may be first neighbors, second neighbors, etc. FIGS. 19a and 19b
illustrate an operation mode in which a single receiver coil 62 is
used to detect the eddy currents generated by three probe
assemblies.
[0138] In this mode of operation, a first group of probe assemblies
202-222 is excited at a first instance of time, i.e. the
transmitter coils 60 of the probe assemblies contained in the first
group are excited to each generate an eddy current while the
remaining probe assemblies are not excited. In the illustrated
embodiment, the first group comprises probe assemblies 202, 204,
206, 214, 216, and 218, which are divided into a first set
containing probe assemblies 202, 204, and 206 and a second set
containing probe assemblies 214, 216, and 218. The two sets of
excited probe assemblies are spaced apart by at least one
non-excited probe assembly. In the illustrated embodiment, three
non-excited probe assemblies, i.e. probe assemblies 208, 210, and
212, are located between the two sets of excited probe
assemblies.
[0139] At the first instance of time, the transmitter coils 60 of
the first and second sets of probe assemblies are excited but only
one receiver coil 62 per set of excited probe assemblies is used
for sensing the eddy currents. In an embodiment in which a set of
excited probe assemblies comprises an odd number of probe
assemblies, only the receiver coil 62 of the central excited probe
assembly may be used for sensing the eddy current. In the
illustrated embodiment and respective to the first set of excited
probe assemblies, only the receiver coil 62 of the probe assembly
204 is used for sensing the eddy currents generated by the probe
assemblies 202, 204, and 206. Similarly and respective to the
second set of excited probe assemblies, only the receiver coil 62
of the probe assembly 216 is used for sensing the eddy currents
generated by the probe assemblies 214, 216, and 218.
[0140] At a second instance of time, a second group of probe
assemblies is excited. For example, the probe assemblies of the
second group may correspond to the probe assemblies of the first
group shifted by one position towards to the right, i.e. the second
group comprises probe assemblies 204, 206, 208, 216, 218, and 220.
The second group comprises a first set of excited probe assemblies,
i.e. probe assemblies 204-208, and a second set of excited probe
assemblies, i.e. probe assemblies 216-220. For the first and second
sets, only the receiver coil 62 of the central probe assembly, i.e.
probe assembly 206 and 218 respectively, is used for sensing the
induced eddy current. It should be understood that after exciting
the second group at the second instance of time, a third group of
probe assemblies is excited at a third instance of time, a fourth
group of probe assemblies is excited at a fourth instance of time,
etc.
[0141] Using the operation mode illustrated in FIGS. 19a and 19b, a
larger magnetic field is generated in the material since a
plurality of neighbor probe assemblies are concurrently excited. In
the presence of an irregular surface to be inspected, such as a
surface comprising a weld crown, concurrently exciting neighbor
transmitter coils allows inducing a more uniform magnetic field
(and thus a more uniform eddy current distribution) at the surface
of the material being inspected when compared to a single large
transmitter.
[0142] In one embodiment, the receiver coil 152 of the central
probe assembly of each set may be used for sensing the eddy current
and determine the length of a defect.
[0143] While in the operation mode of the array probe 200
illustrated in FIGS. 18a and 18b a single receiver coil is used for
measuring the eddy current generated by an excited probe assembly,
it should be understood that other configurations may be possible.
For example, at least two adjacent or neighbor receiver coils may
be used for sensing the eddy current induced within the material to
be inspected by a single transmitter coil. FIGS. 20a and 20b
illustrate an operation mode of the array sensor 200 in which three
neighbor receiver coils 62 are used for sensing the eddy current
induced by a single transmitter coil 60.
[0144] In this mode of operation, a first group of probe assemblies
202-222 is excited at a first instance of time, i.e. the receiver
coils 62 of the probe assemblies contained in the first group are
activated to each sense an eddy current while the remaining probe
assemblies are not excited. In the illustrated embodiment, the
first group comprises probe assemblies 202-206, 210-214, and
218-222, which are divided into a first set containing probe
assemblies 202, 204, and 206, a second set containing probe
assemblies 210, 212, and 214, and a third set comprising probe
assemblies 218, 220, and 220. Two successive sets of excited probe
assemblies are spaced apart by at least one non-excited probe
assembly. In the illustrated embodiment, a single non-excited probe
assembly, i.e. probe assemblies 208 and 216, is not excited between
two sets of excited probe assemblies.
[0145] At a first instance of time and for each set of excited
probe assemblies, the transmitter coil 60 of a single excited probe
assembly is excited to generate an eddy current which is sensed by
the receiver coil 62 of each excited probe assembly contained in
the set. In an embodiment in which a set of excited probe
assemblies comprises an odd number of probe assemblies, only the
transmitter coil 60 of the central excited probe assembly may be
used for inducing the eddy current within the material. In the
illustrated embodiment and respective to the first set of excited
probe assemblies, only the transmitter coil 60 of the probe
assembly 204 is excited for inducing an eddy current which is
sensed by the receiver coil 62 of the excited probe assemblies
202-206. Respective to the second set of excited probe assemblies,
only the transmitter coil 60 of the probe assembly 212 is excited
for generating an eddy current while the receiver coils 62 of the
excited probe assemblies 210-214 are used for sensing the eddy
current. Respective to the third set of excited probe assemblies,
only the transmitter coil 60 of the probe assembly 220 is excited
for generating an eddy current while the receiver coils of the
excited probe assemblies 218-222 are used for sensing the eddy
current.
[0146] At a second instance of time, a second group of probe
assemblies is excited. For example, the probe assemblies of the
second group may correspond to the probe assemblies of the first
group shifted by one position towards to the right, i.e. the second
group comprises probe assemblies 204-208, 212-216, and 220-222. It
should be understood that the second group also comprises a further
probe assembly which is adjacent to the probe assembly 222 and is
not illustrated in FIG. 20b. The second group comprises a first set
of excited probe assemblies, i.e. probe assemblies 204-208, a
second set of excited probe assemblies, i.e. probe assemblies
212-216, and a third set of excited probe assemblies, i.e. probe
assemblies 220 and 222 and the probe assembly which is adjacent to
the probe 222 and does not appear on FIG. 20b. For each set, only
the transmitter coil 60 of the central probe assembly, i.e. probe
assembly 206, 214, and 222 is used for inducing an eddy current
within the material while the receiver coil 62 of all of the probe
assemblies contained within the set are used to sense the eddy
current. For the third set, only the transmitter coil 60 of the
excited probe assembly 222 is used for inducing an eddy current. It
should be understood that after exciting the second group at the
second instance of time, a third group of probe assemblies is
excited at a third instance of time, a fourth group of probe
assemblies is excited at a fourth instance of time, etc. It should
be noted that the voltages measured at the receiver coils of a same
set may be added together., at each instance of time
[0147] In one embodiment, a probe may comprise at least two array
probes 200. The relative position between the two array probes may
vary. For example, the two array probes may be aligned along the
scan direction, i.e. the two array probes are positioned
side-by-side along the scan direction. In this case, the
longitudinal axes of the transmitter coils of the two array probes
200 are all parallel to the scan direction, and the two array
probes are positioned side-by-side along the scan direction. In a
further example, the two array probes may be misaligned. In this
case, the axes of the two array probes are not parallel and
intersect one another at a given angle.
[0148] FIG. 21 illustrates two array probes 230 and 232 which are
positioned side-by-side along the scan direction and transversally
shifted. The array probe 230 is shifted to the left with respect to
array probe 232 along a transversal axis, i.e. an axis orthogonal
to the scan direction. Such a configuration allows a better
precision since the probe assemblies of the array probe 232 will be
able to detect any defect that could extend between two adjacent
probe assemblies of the array probe 230. In this embodiment, the
shift corresponds to half the width of a probe assembly. For
example, if a probe would comprise three array probes, the shift
between two array probes could be equal to one third of the width
of a probe assembly.
[0149] In one embodiment, the probe further comprises a motion or
position sensor for determining the positon of each probe element
or assembly at each instance of time during the scan. Information
such as the positon of a defect and/or the ends of a defect may
then be obtained using the positon information provided by the
motion or position sensor.
[0150] While the present description refers to a receiver coil for
sensing an eddy current, it should be understood that any other
adequate device adapted to detect an eddy current may be used.
Examples of adequate devices comprise Hall effect sensors or
magneto-resistance sensors such as Giant MagnetoResistive (GMR)
sensors, Tunnel MagnetoResistive (TMR) sensors, Colossal
MagnetoResistive (CMR) sensors, Anisotropic MagnetoResistive
sensors, or the like.
[0151] It should be understood that some of the characteristics of
the above-described probe element or assembly may be varied. For
example, while it comprises a single transmitter coil, it should be
understood that the above-described probe element may comprise at
least two transmitter coils, as illustrated in FIG. 22. In this
case, the central section of the core is provided with a first
transmitter coil while each leg of the core is also provided with a
respective transmitter coil. The three transmitter coils cooperate
to generate a magnetic field between the legs of the core. It
should be understood that no transmitter coil may be mounted on the
central section of the core, as illustrated in FIG. 23. In this
case, the probe assembly comprises two transmitter coils each
mounted on a respective leg of the core for generating a magnetic
field between the two legs.
[0152] While the above-described core 52 is provided with two legs
extending substantially orthogonally from a central section, it
should be understood that other shape for the core may be possible.
For example, a curved tubular core may be used to receive a
transmitter coil thereon as illustrated in FIG. 24. It should be
understood that more than one transmitter coil may be mounted on a
curved core.
[0153] While the above description refers to the use of a magnetic
core on which at least one transmitter coil is mounted, it should
be understood that a non-magnetic core may also be used. FIG. 26
illustrates a non-magnetic prism on which a single transmitter coil
is mounted while FIG. 27 illustrates a non-magnetic prism on which
three transmitter coils are mounted.
[0154] FIG. 28 illustrates the distribution of eddy current density
when a single probe element 50 is used to generate a magnetic field
within a material to be inspected. FIG. 29 illustrates the
distribution of eddy current density when an array probe comprising
three probe elements 50 is used to generate a magnetic field within
the material. Increasing the number of probe elements allow to
create a larger magnetic field within the material.
[0155] FIG. 30 (prior art) shows the eddy current density
distribution as induced by a single, large transmitter in a
material to be inspected. In the presence of an irregular surface,
such as a weld crown, the field density is higher in portions of
the surface that are closer to the transmitter, like the weld crown
in this case, and lower in the heat-affected zone where cracks may
be located, thus decreasing the defect detection performance.
[0156] FIG. 31 illustrates the distribution of eddy current density
when an array probe comprising five probe elements 50 is used to
generate a magnetic field within the same material as the one of
FIG. 30. The eddy current induced by the array probe of FIG. 31 is
more focalized with respect to that of FIG. 30.
[0157] As will be readily understood, although the example
embodiments have been described in relation to a probe body with a
planar configuration of coil elements, one will readily understand
that the linear configuration of coil elements on one or more
transversal rows of coil elements can be provided in a non-planar
arrangement.
[0158] For example, should a cylindrical or semi-cylindrical probe
body be needed for the inspection of a material, for example in the
case of the inspection of a tube, the linear configuration of coil
elements can be arranged to follow the curved outer surface of the
probe body, the linear configuration of coil elements forming a
curved ribbon or annulus (which may be partial). The curvature
and/or general shape of the surface created by the coil elements
placed side-by-side need not be regular, symmetrical or planar. The
height of each coil element with respect to its neighboring
elements may vary, even if they are identical.
[0159] In one embodiment, the above-described eddy current array
probe is capable of detecting longitudinal and transverse
surface-breaking defects in metallic objects. It allows for
determining the depth and/or length of longitudinal
surface-breaking defects. The detection and sizing capabilities are
possible even in the presence of non-conductive coating on the
surface being inspected. The probe features several independent
coil configurations such that, at a given frequency, orthogonality
exists between a defect response and the lift-off response.
[0160] This coil arrangement allows measuring independently and
simultaneously lift-off variations (along a horizontal axis) and
amplitude variations originating from a defect response (along a
vertical axis). In one embodiment, a variable number of
transmitters can be excited simultaneously to induce magnetic
fields with varying extent in the material being inspected. Such
magnetic fields are generating eddy current distributions in the
material being inspected. It is possible to adjust the density of
the eddy currents to accommodate for specific geometric
circumstances by exciting a certain number of transmitters in the
probe. The present probe can induce uniform eddy current
distributions even in irregular geometries, such as weld crowns.
The intensity and distribution of eddy currents induced by a probe
can be adjusted to suit many different geometric conditions and
provide an adjustable sensitivity to surface-breaking defects.
EXAMPLE
[0161] In an example embodiment, an Eddy Current Array Probe for
Carbon Steel Weld Inspection is provided. The probe leverages the
power of eddy current array (ECA) technology to ascertain the
length and depth of surface-breaking cracks in carbon steel welds
without any surface preparation. Unlike traditional methods such as
magnetic particle testing (MT) and penetrant testing (PT), the
present array probe eliminates the need to strip off paint and
coating over joints. The present array probe can tolerate a
lift-off of up to 3 mm (0.120 in.). The width of the probe enables
its spring-loaded "fingers" to adapt to the weld crown so that it
can scan the complete weld cap, toe area, and heat-affected zone in
a single pass with high, uniform sensitivity all the while sizing
cracks as deep as about 10 mm.
[0162] Ferrous materials have always been a challenge for eddy
currents. In one embodiment, the present array probe leads to a
whole range of probes, for various weld configurations and defect
sizes, capable of addressing at least some needs of many industries
relying heavily on carbon steel.
[0163] In one embodiment, the present array probe allows increasing
scanning speed. For example, welds may be examined up to 10 times
faster compared to existing electromagnetic methods. In one
embodiment, the use of the present array probe yields a wealth of
information through 2D and 3D C-scans. This imaging offers
intuitive and visual indications of defects, giving an operator
confidence in his inspection results.
[0164] While in the above description, each probe element comprises
at least one transmitter for inducing an eddy current within a
material to be inspected and at least one receiver for sensing the
induced eddy current, it should be understood that a single coil
may be used to both generate the magnetic field and sense the eddy
current. The longitudinal axis of the single coil is then parallel
to the surface of the material to be inspected and orthogonal to
the induced eddy current.
[0165] The embodiments of the invention described above are
intended to be exemplary only. The scope of the invention is
therefore intended to be limited solely by the scope of the
appended claims.
* * * * *